This ZRO4 annual replacement filter 4 pack includes one, five micron sediment filter, one, five micron carbon block filter, one 50 gallon per day membrane and one 10 in inline GAC filter. The sediment filter traps sediment and other particulate matter, such as dirt, silt and rust which affect the taste and appearance of the water. The 5 Micron filtration rating is in the particle filtration category and is equivalent in size to milled flour. The five micron carbon block filter reduces chlorine, objectionable tastes and odors. The 50 gallons per day semi permeable membrane effectively reduces total dissolved solids and sodium as well as a wide range of contaminants such as arsenic, lead, perchlorate, chromium, copper, radium and protozoan cysts, giardia and cryptosporidium. The heart of the reverse osmosis system reduces impurities down to 1/10,000 of a micron.